Which two states form the western border of Pennsylvania?

The Keystone State's western edge is defined by two different neighbors (Review). The majority of this boundary is a long, straight north-south line shared with the state of Ohio. Further south, Pennsylvania's border meets the Northern Panhandle of West Virginia, a narrow and distinctive strip of land that extends northward along the Ohio River.

This unusual panhandle is a fascinating relic of colonial-era land claims and surveys. It is famously squeezed between the straight western line of Pennsylvania and the meandering path of the Ohio River, which forms the panhandle's own western edge. Because of this geography, someone in the panhandle town of Weirton, West Virginia, is actually farther east than Pittsburgh, Pennsylvania.

The straight, surveyed line that separates Pennsylvania from Ohio also has its own history. Known as Ellicott's Line, it was meticulously mapped in 1785 by surveyor Andrew Ellicott. This meridian was a crucial starting point for the subsequent surveying of the Northwest Territory, demonstrating how the careful drawing of these early state boundaries was fundamental to the westward expansion of the United States.